Research and development regarding next generation mobile communication systems has been proceeding in this technical field. The W-CDMA (Wideband Code Division Multiple Access) standardization organization 3GPP (3rd Generation Partnership Project) has been discussing a communication system called Long Term Evolution (LTE) as a successor of W-CDMA, HSDPA (High Speed Downlink Packet Access), and HSUPA (High Speed Uplink Packet Access). As a radio access scheme in LTE, Orthogonal Frequency Division Multiplexing (OFDM) is under consideration for downlink, and Single-Carrier Frequency Division Multiple Access (SC-FDMA) is under consideration for uplink (see 3GPP TR 25.814 (V7.0.0), “Physical Layer Aspects for Evolved UTRA”, June 2006, for example).
In OFDM, a frequency band is divided into plural narrow frequency bands (sub-carriers), and data are placed on the respective divided frequency bands to carry out transmission. The sub-carriers are densely arranged in a frequency direction, allowing the sub-carriers to be partly overlapped without causing interference, thereby realizing high speed transmission and improving frequency usage efficiency.
In SC-FDMA, a frequency band is divided into plural narrow bands, and different narrow bands are used by different user terminals, so that interference between the user terminals can be reduced. According to SC-FDMA, which is characterized in that variations in the transmission power are reduced, a large coverage area and low energy consumption in the user terminal can be realized.
In LTE, one or more physical channels for both uplink and downlink are shared by plural user terminals (plural sets of user equipment). The channel which is shared by plural user terminals is typically called a shared channel. In LTE, a Physical Uplink Shared Channel (PUSCH) is used as a shared channel for uplink and a Physical Downlink Shared Channel (PDSCH) is used as a shared channel for downlink.
In a communication system using these shared channels, the base station apparatus needs to signal information about user terminals to which the shared channel is allocated for each sub-frame (1 ms in LTE). A control channel used for this signaling is called a Physical Downlink Control Channel (PDCCH) or a Downlink L1/L2 Control Channel (DL-L1/L2 Control Channel). Information on the PDCCH includes downlink scheduling information, acknowledge information (ACK/NACK), an uplink scheduling grant, an overload indicator, a transmission power control command bit, and so on, for example (see 3GPP,R1-070103, “Downlink L1/L2 Control Signaling Channel Structure”, for example).
The downlink scheduling information and the uplink scheduling grant correspond to the information about user terminals to which the shared channel is allocated. The downlink scheduling information includes allocation information for downlink resource blocks (RBs) on the downlink shared channel, a user equipment identification (UE ID), the number of streams for MIMO (Multiple Input and Multiple Output) transmission, information about a precoding vector, a data size, a modulation scheme, information about hybrid automatic repeat request (HARQ), and so on, for example. The uplink scheduling grant includes allocation information for uplink resources on the uplink shared channel, a UE ID, a data size, a modulation scheme, information about uplink transmission power, information about a demodulation reference signal for uplink MIMO transmission, and so on, for example.